Introduction

IntelliJ IDEA provides a built-in debugger for your client-side JavaScript code that works with Chrome. The video and the instructions below walk you through the basic steps to get started with this debugger.

Debugging an application running on the built-in server

IntelliJ IDEA has a built-in web server that can be used to preview and debug your application. This server is always running and does not require any manual configuration. All the project files are served on the built-in server with the root URL http://localhost:<built-in server port>/<project root>, with respect to the project structure.

Open the HTML file that references the JavaScript to debug or select the HTML file in the Project view.

On the context menu of the editor or the selection, choose Debug <HTML_file_name>. IntelliJ IDEA generates a debug configuration and starts a debugging session through it. The file opens in the default browser, and the Debug tool window appears.

To save the automatically generated configuration for further re-use, choose Save <HTML_file_name> on the context menu after the debugging session is over.

Example

Suppose you have a simple application that consists of an index.html file and a MyJavaScript.js file, where index.html references MyJavaScript.js. To start debugging this application using the built-in server, open index.html in the editor and choose Debug 'index.html' on the context menu: IntelliJ IDEA creates a run/debug configuration automatically, and a debugging session starts: To restart the new run/debug configuration, click in the upper right-hand corner of the IntelliJ IDEA window or choose Run | Debug on the main menu:

Debugging an application running on an external web server

Often you may want to debug client-side JavaScript running on an external development web server, e.g. powered by Node.js.

Run the application in the development mode. Often you need to run npm start for that. When the development server is ready, copy the URL address at which the application is running in the browser - you will need to specify this URL address in the run/debug configuration.

Create a debug configuration of the type JavaScript Debug: Choose Run | Edit Configuration on the main menu, click the Add New Configuration button on the toolbar, and select JavaScript Debug from the pop-up list.

In the Run/Debug Configuration: JavaScript Debug dialog box that opens, specify the URL address at which the application is running. This URL can be copied from the address bar of your browser as described in Step 2 above. Click OK to save the configuration settings.

Choose the newly created configuration in the Select run/debug configuration drop-down list on the toolbar and click the Debug toolbar button . The URL address specified in the run configuration opens in the chosen browser and the Debug tool window appears.

Debugging asynchronous code

IntelliJ IDEA supports debugging asynchronous client-side JavaScript code. The asynchronous debugging mode is toggled through the Async check box on the tool bar of the Debugger tab in the Debug tool window. The check box is displayed only during a JavaScript debugging session.

When this check box is selected, IntelliJ IDEA recognizes breakpoints inside asynchronous code and stops at them and lets you step into asynchronous code. As soon as a breakpoint inside an asynchronous function is hit or you step into asynchronous code, a new element Async call from <caller> is added in the Frames pane of the Debugger tab. IntelliJ IDEA displays a full call stack, including the caller and the entire way to the beginning of the asynchronous actions.

When the check box is cleared, IntelliJ IDEA does not recognize and therefore skips breakpoints in the asynchronous code and does not allow you to step into it.

The image below shows an example of a JavaScript debugging session.

With the Async check box selected, the debugger will stop at line3(breakpont), then at line5(breakpoint). On clicking Step into, the debugger will stop at line5 (on function), then will move to line6.

With the Async check box cleared, the debugger will stop at line3(breakpont), then at line5(breakpoint). On clicking Step into, the debugger will move to line9.

Choose the newly created configuration in the Select run/debug configuration drop-down list on the tool bar and click the Debug toolbar button .

The HTML file specified in the run configuration opens in the chosen browser and the Debug tool window opens with the Frames drop-down list showing all the Workers:

To examine the data (variables, watches, etc.) for a Worker, select its thread in the list and view its data in the Variables and Debug Tool Window. Watches panes. When you select another Worker, the contents of the panes are updated accordingly.